The removal of snow at airports is of social and economical relevance. Airport downtime costs are in the order of tens of thousands Euros per minute for hub airports.
The scale of snow removal varies according to airport size and geographic location. The snow removal operation of Amsterdam Airport Schiphol (AAS) is taken as a reference case. AAS handles the following guidelines for their snow removal operation:
1. AAS remains open for air traffic as long as possible.
2. AAS strives to the least amount disruptions as possible for the airport operations.
3. After calamities the fight on snow and slipperiness has the highest priority.
4. All assigned staff will be employed for this purpose.
At an airport the tarmac to be cleared can be categorized in runways, exits, taxiways and platforms. These can be released when they are cleared of snow and the tarmac again complies to the operating standards of AAS. A runway is fully in operation again when the entire surface is cleared of snow. This includes the exit at the head and tail of the runway, the second and third rapid exit, and the taxiway parallel to the runway.
In FIG. 1 the definition of a runway, exit, rapid exit and a taxiway is schematically illustrated. The dimensions differ per runway, but the given dimensions in FIG. 1 give a good estimation of the size. The shoulders are not illustrated, typically they are a third of the width of a runway, taxiway or exit.
A platform is the place where airplanes are parked during boarding, a schematic view of a platform is given in FIG. 2.
The coefficient of friction μ between an airplanes' tire and the runway must be greater or equal to 0.25. Where μ is defined as the ratio between the friction force and the normal force. If the coefficient of friction after clearing is smaller than 0.25 the runway has to be cleared again. This criteria is not equal for all airports. The US Federal Aviation Administration (FAA) advises a minimum μ of 0.26. The FAA advises US airports through Advisory Circulars. Some are guidelines and some are mandatory.
AAS has different standards for runways, exits, taxiways and platforms. For runways these are:                1) At least one runway should be operational with a μ≧0.25 and with a guaranteed capacity of 30 starts or landings per hour.        2) 23:00-6:00 (local time): At unfavorable conditions a number of starts could be postponed until the runway is cleared of snow.        3) 5:30-23:00 (local time): Within 40 minutes after passing of the snow precipitation or freezing rain a second runway must be operational.        
For exits and taxiways the friction coefficient must be μ≧0.25 and the maximum thickness of the layer of contamination is 4 mm. Contamination is the collective for snow, slush, water and chemicals. For a platform there is no criterion for the surface friction. Depending on the location of the platform it must be completely or partially cleared of snow and ice.
Airports have different kinds of equipment for snow removal. A Runway Sweeper (RS) is a transformed truck that removes the snow in three stages. First a blade plow plows the majority of the snow towards the side. Then a broom clears the tarmac of snow, which is compressed between the pores of the tarmac and finally a blower blows the last remains to the side. An example of a runway sweeper includes a truck with a hitched broom is called a Hitched Broom Truck (HBT). The function of the HBT is to brush the tarmac. An example of an HBT includes blade plows that have limited casting range and are not capable of displacing very deep or very hard snow. This has led to the development of rotating cutting devices with one or more rotating elements. All designs of Rotary Plows (RP) cut the snow by means of a rotating element on the right side and on the left side a blade plow. The function of this blade plow is to remove the snow from the vicinity of the landing lights and prevents the RP of damaging the landing lights. Potassium Formate (PF) is sprayed on the runway. The goal of PF is to decrease the freezing point of H2O. The concentration of PF in H2O is proportional to the decrease in freezing point, therefore PF is sprayed when the majority of snow is removed from the runway.
For the removal of snow from runways, taxiways and exits there are two snow fleets used at AAS. The AAS snow feet includes the following vehicles and persons: 1 manager, 1 coordinator, 8-runway sweepers including operators, 1 blade plow including operator, 1 rotary plow including operator, 1 hitched broom truck including operator, and 1 sprinkler machine including operator.
The manager has the general overview of a snow fleet and a coordinator controls the individual machines. A snow schematic view of the snow fleet in operation is given in FIG. 3.
In this example, if a snow fleet removes snow from a taxiway the number of runway sweepers is decreased to 5. The majority of the snow on a platform is removed by blade plows and the last remains by HBT's. In FIG. 2 a platform is shown, in addition to the route of the blade plows and HBT's, with the snow deposit area.
Airports apply different kind of methods depending on the weather conditions. These methods are:                1) Preventive mechanical removal: When frost is expected any water pools that might be present are removed. This will be done by HBT's on runways, exits, taxiways and platforms.        2) Mechanical removal: In the case of snow, slush, hail or pieces of ice the removal will be done by a snow fleet. Slush is a mixture of ice and water. In case of dry or extreme snowfall, mechanical removal of snow is assumed to be better than spraying potassium formate. In the last case there is a chance that the dry snow might stick to the liquid and forms a layer difficult to remove.        3) Preventive spraying of potassium formate: The prevention of frost on runways, exits and taxiways. On the tarmac an amount of 25 g/m2 of potassium formate will be sprayed. If hail precipitation is expected the amount will be increased to 40 g/m2.        4) Corrective spraying of potassium formate: The removal of hail, frost or frozen slush on the runway, exit and platforms. The amount of potassium formate to be sprayed is 40 g/m2. This is an emergency measure.        5) Corrective scattering of de-icing grains: The removal of ice from the tarmac, after which the mechanical removal method can start. This is an emergency measure.        6) Sand scattering: The sand will make the ice surface rough. This is a final emergency measure.        
In the early twentieth century snowplows made their entry due to the motorization. In 1927 for example the company Good Roads advertised for snowplows that could be mounted on every truck.
The focus of improving snow removal is on four main criteria that include:                1) Decrease emissions. ACI Europe is the council of over 400 European airports. In 2009 ACI Europe launched the Airport Carbon Accreditation program. The member airports committed to the ultimate goal of becoming carbon neutral. A decrease of emissions will imply a decrease of fuel use. This means the required tank time per snowfall can be decreased which has a positive side effect on the operational costs.        2) Decrease costs. At the moment the capital expenditures (CAPEX) of a snow fleet are between 8 and 9 million Euros and the economic lifetime is 15 years. Furthermore the snow removal machines are dead capital for most time of the year. The current technology results in high operational expenditures (OPEX) due to two characteristics. One snow fleet includes 12 operators and 2 managers, the companion and the coordinator. A decrease of machines will lead to a decrease in labor costs. And the downtime costs of tens of thousands of Euros lead to high OPEX. A faster operation will decrease these downtime costs.        3) Decrease organizational complexity. FIG. 3 shows the formation of a snow fleet. It is essential the snow fleet holds this formation over the entire runway. This requires intensive training of the personnel. The main concern of the snow removal staff is to manage this organizational complexity. A decrease in the number of operators will simplify the operation.        4) Increase capabilities. An airport is mandatory to remove the Foreign Object Debris (FOD) from the runway. Examples of FOD are small stones, nuts and bolts. At the moment the FOD removal operation is done by other machines. A combination of to multiple tasks in one machine will have a positive effect on costs and the operational complexity. The current substitute technique and the improved technique will be assessed on these main criteria. The current substitute technique is heated pavements.        
Centerline lights indicate the centerline of the runway to pilots and are shown in FIG. 4. These centerline lights are slightly sunk in the runway, but can still form an obstacle for plows. The dimensions of a center light are given in FIG. 4. AAS noted in the winter of 2010/2011 a significant damage to center lights.
The FAA and the US Department of Defense (DOD) combined their regulations for surface drainage design. The maximum transverse slope is 2% and is a trade off between drive comfort and drainage. FIG. 5 shows the consequence of the transverse slope. A plow, or multiple plows, must follow this slope.
Airfield signage is intended to provide information and direction to pilots. For example, a sign tells the pilot he is on taxiway R and the arrow indicates him where he will intersect taxiway W2. According to the FAA, post-clearing operations must be conducted to ensure the visibility of airfield signage. The distance of these signs from the pavements edge depends on its size. According to the FAA this is between 3 and 18 meters, ranging from the smallest to the largest sign.
All existing heated pavement technologies are characterized by the transfer of heat from an energy source to the tarmac. Geothermal energy is the most utilized energy source. In 2010, 423,830 TJ of geothermal energy was used globally. This is a yearly increase of 9.3% since 1995. In 2010 the fraction of geothermal energy used for snow melting applications was 0.44%, which is 1,845 TJ. The applications are limited to Argentina, Japan, Switzerland, Iceland and the United States. 78% of the total energy used for snow melting is applied in Iceland. The costs of energy for passive methods depends significantly on the available local natural resources.
FIGS. 6A-6B show the basics of an aquifer thermal energy storage (ATES) system. In summer water from the cold aquifer can be applied for cooling and in winter this works vice versa. It contains at least two boreholes that lead to suitable aquifer layers where groundwater is stored. A suitable aquifer layer is high permeable and the groundwater it contains is flowing slow. ATES can be fully automated in order to minimize operational activities in winter. An additional advantage of a heating system is the reduction of seasonal temperature fluctuations. This will increase the lifetime of the tarmac.
The input temperature of the groundwater from the warm aquifer in winter is about 15° C. at AAS. The required temperature of the heat transfer fluid for the most extreme snowfall in the past twenty years is 65° C. A conventional ATES system normally comprises a heat pump to heat the water up to a maximum of 40° C. If an extreme snowfall occurs additional heating by, for example, a boiler is required.
It is assumed the ATES system can be installed during the normal renovation of the runways tarmac. Downtime costs due to installation are therefore excluded in the investment. Heated pavement technology is not competitive with the current technology based on the first two criteria, the decrease of emissions and costs.
What is needed is a snow removal system and method that addresses the challenges to decrease emissions, decrease costs, and decrease the organizational complexity.
Untouched snow is a material easy to handle. However once it is touched, mixed with chemicals and when it is aged it is not. The amount of energy on plowing is proportional to the mass of the snow in front of the plow. It is also the only variable that can be altered, since the dynamic friction coefficient between snow and tarmac is constant for a certain snow type. A decrease of emissions can therefore be realized by taking the snow directly off the tarmac. What remains is the energy on brushing and blowing. If the new technique can take off the snow directly from the tarmac and fulfills the μ≧0.25 criterion, brushing and blowing will become superfluous. The challenge to decrease the organizational complexity is a function of the snow removal operation. This complexity is a consequence of the amount of operators, that need to be managed under time pressure. If the amount of operators can be decreased this will lead to an organizational simplification.
What is further needed is a system and method that enables other features than snow removal to be implemented. On a runway multiple tasks are performed. These tasks include FOD removal, friction measurements and tarmac status measurements. The most frequent and time-consuming runway operation is FOD removal. AAS for example removes its FOD every night. This requires several hours per runway, including exits and the parallel taxiway.